Fractionation system



Egg i=0 W; H BAHLKE ET AL 15947 577 FRACTIONATION SYSTEM Filed May 21., 1931 Jrwaniorw- WZZZZamfiBQhZ/QQ Ernest W 772mm ATTORNEY Patented Feb. 20, 1934 n I r 1,947,577

UNITED ,STATES PATENT orrlce FRACTIONATION SYSTEM William H. Bahllre, Hammond, Ind., and Ernest W. Thiele, Chicago, Ill., assignors to Standard Oil Company, Chicago, 111., a corporation of Indiana Application May 21, 1931. Serial No. 538,912

4 Claims. (Cl. 261-114) This invention pertains to improvements in means of lugs or brackets 22 welded or otherwise columns for the fractionation of volatile liquids, secured to the shell of the columnand, more particularly, means for breaking up Although our invention is applicable to any froth or foam formed in fractionating columns type of column within which there is formed a operating under pressure as in pressure distilla froth or foam which must be separated into'its 60 tion of hydrocarbonoils. constituent vapors and liquid to obtain the, most The efficiency of fractionating columns in efficient fractionation, for the pu p e f l cracking systems is frequently greatly reduced tration we will describe the operation of our inbecause of frothing or foaming of the liquid on vention in a fractionating column in a hydrothe fractionating trays. This trouble is probably on 11 a i SYStBITL.

attributable to the fact that under the pressure In practice, our invention operates as follows: conditions existing within the column the specific Hot hydrocarbon oil vapors from a pipe still or gravities of the liquid and of the vapors are of reaction chamber (not shown) at 850-900 F. and the same order of magnitude, and in bubbling under 300-325 lbs. gage pressure enter fractionl through the liquid,'the vapors, instead of passsting column 10 through a vapor line in the lower 7 ing therethrough asthey normally do, exert a part of the column (not shown). :The vapors buoyant force on the liquid producing a froth or ascend within the column through, vaporpas foam. For eflicient fractionation it is necessary sages 16 andbubble caps 17 and are fractionated to break up this froth or foam, and separate the therein, the heavier constituents condensing in 23 vapors from the liquids. ,Our invention effectivethe lower sections of the column and part of the 76 1y accomplishes this, and will be fully understood lighter condensible constituents condensing in from the ;following description illustrated by the the upper sections of the column to form a reflux accompanying drawing in whichwhich flows to the fractionating trays 1 1 and Figure-1 is a section through 1--1 of Figure 11a through which the ascending vapors are 2 of an increment of a fractionating column bubbled. The constituents not condensible at equipped with our foam breaking device. the temperatures within the column are taken Figure2 is a section through 22 of Figure off overhead through a vaporline (not shown) 1, in which,- like parts are indicated by similar We have found that fractionating columns opreference characters. erating under pressureas described may become 30 Figure 3 is a section of a fractionating colclogged with foam, even at vapor velocities, which umn showing a modified form of our invention. would permit perfectly satisfactory operation at Referring to Figuresv 1 and 2 of the drawing, other conditions. Thus, at vapor velocities-of as a fractionating column 10 of the conventional low as one-half foot per second, foaming may type contains aplurality of fractionating trays occurv and, of course, the difficulty is increasedat 11. and Ila-constructed in sections A, B,- C, sehigher rates of'operation I v cured together by bolts 12 and supported in the The foam so produced, togethenwith thliqcolumn by rings 13 welded or otherwise secured uid on the trays 11 and 11a,.etc., overflows dams to theshell of column 10. The upwardly turned 14 through pipes 18 and enters chambers 19 flangesbetween sections-A and B, and B and C wherein the foam, out of contact with the as- 4 form dams or weirs 14 and 15, the height of cending vapors and in quiescent. state, is sepa- 9 5 which determines the height of the liquid level rated into its component liquid and vapor. The on each tray. Each of the fractionating trays separated vapors within the quiescent areas 19 11, 11a, etc. is provided with vapor passages 16 are removed therefrom through vapor outlets 21 covered by bubble caps 1'? which are perforated to the vapor space above tray 11, and the separat- I 4 or serrated at the bottom thereof to allow the ed liquid freed from admixed vapors, are removed vapors to bubble out through the liquid on the from chamber 19 through drain 20 which extends tray, and a liquid downfiow pipe 18 which combelow the liquid level of the subjacent tray. municated with an enclosed chamber or reser- A modified form of our invention is shown in voir 19 Within the column and spaced between Figure 3 in which we have shown a section of a t adjacent trays. Each reservoir is provided with fractionating column 23 in a cracking unit. Cola drain pipe 20 leading to the subjacent tray and umn 23 is equipped with a plurality of fractionatextending below the liquid level of said tray, and ing trays 24 which are constructed in sections a vapor line or vent 21 extending into the vapor 24A, 24B and 240, secured together by bolts 25. space above the tray above said reservoir 19. The These sections form pools for incoming liquid and 1 reservoirs may be supported in the column by flanges 26 and 2? act as weirs to determine the 0 depth of the liquid on each tray. Each tray is provided with a subjacent foam chamber 28 which may be an integral part of the fractionating plate 24 and through which risers 29 lead the vapors from the plate below to the bubble caps 30. The fractionating trays 24 are sealed to the walls of the column in the conventional way, and may be supported in the column by any suitable means, for example, by brackets or lugs 31 welded or otherwise secured to the walls. Each tray 24 communicates with the reservoir 28 formed by said fractionating tray 24 and its subjacent plate 28A by means of opening 32. Each reservoir 28 is provided with a vapor outlet 33 communicating with the vapor space of the fractionating tray above, and a liquid outlet 34 extending below the liquid level of the subjacent fractionating tray.

In the operation of this modified form of fraction'ating columns, vapors from a pipe still or a reaction chamber in a cracking system for the conversion of hydrocarbon oil, enter the fractionating column 23 through a vapor inlet (not shown) at an intermediate point near the base of the column, and pass upward through the vapor passages and under the serrated or perforated bubble caps 30. Under normal operating conditions or conditions when the column is operating at low capacity, the vapors, after leaving the bubble caps, bubble through the reflux liquid on the trays, and thence pass to the trays above. However, under the conditions which exist in the column when operating under pressure of 100-400 pounds, and at normal capacity with avapor velocity of more than say one-half foot per second, a sharp separation of the vapor and liquid does not occur and a froth or foam is produced on the trays. The frothy mixture of liquid and vapors flows from the trays through the overflow 32 to the reservoir 28 wherein the frothy mixture being out of contact of ascending vapors, is permitted to remain in a quiescent state for a sufficient time to permit it to separate into its component liquid and vapor. The released vapors pass through the vapor outlet 33 into the vapor space of the tray above. The vapor freed liquid flows to the subjacent fractionating tray through the drain line 34.

By the use of the apparatus and method herein described, the efficiency of fractionating columns, in which conditions are favorable for the formation of froth or foam on the trays, is substantially increased. It is to be noted that the vapors separated in the quiescent regions are introduced into the space above each tray substantially free of entrained liquid particles which results in a cleaner fractionation.

By the present invention, fractionation is improved by avoiding entrainment which gives a better quality of distillate, and in addition, column capacities are substantially increased.

descending liquid and a froth is produced, a. plurality of independent chambers, means for collecting said froth from each one of said trays and means for passing said froth to one of said chambers out of contact with the ascending vapors wherein said froth is allowe'l'to separate into its component liquid and vapor, and means for separately discharging liquids and vapors from each of said chambers.

2. In a f'ractionating column containing a plurality of fractionating trays wherein ascending vapors are co-mingled with descending liquid and a froth is produced, an independent reservoir between each two adjacent trays, means for removing said froth from said trays to said reservoir out of contact with the ascending vapors whereby said froth may separate into its component liquid and vapor, venting means for removing said liquid from said reservoir to the tray below, and venting means for removing said vapors from said reservoir to the vapor space of the tray above.

3. In a fractionating column, means for permitting froth formed by the co-mingling of vapors and liquids to separate into its component liquid and vapors out of contact with the vapors rising in said column, which comprises a quiescent chamber within the fractionating column, an unsealed conduit for feeding said froth to said quiescent chamber, a sealed conduit for introducing said separated liquid to the fractionating tray below said quiescent chamber, and a conduit to lead sa'id separated vapors from the chamber to the vapor space of the fractionating tray above said quiescent chamber.

4. In a fractionating apparatus, a column equipped with fractionating plates, independent chambers in said column spaced between said fractionating plates for receiving frothproduced in the fractionating operation, an unsealed froth inlet entering each of said chambers from the plate above, a vapor outlet from each of said chambers entering the vapor space of the plate above, and a liquid outlet from each of said chambers extending below the liquid level of the plate below.

WILLIAM H. BAHLKE. ERNEST W. THIELE. 

